Second test sample. A lot better! I degassed the epoxy mixture in a vacuum chamber for 30 minutes. I then applied it to the poplar wood together with the fiberglass. I rolled out any air bublles and applied the vacuum:

Simple and cheap vacuum chamber. I used a thick glas jar and a thick sheet of plastic as a lid. I applied some rubber from a car tire to the plastic using tacky tape.

This time using the bag (with a simple diy vacuumconnector)

Result:

No air bubbles can be seen with the naked eye. I am not able to get a nice flat finish, the bag pulls in between the fiber yarns showing dents and revealing the treads connecting the fiber yarns. I need a rough surface since I will be doing the glassing in multiple stages. Sanding is not an option since I will damage the fiberglas yarns. Peelply will be the solution here.

I ordered some peelply, bleeder and breather fabric which I will use for the third test sample. It seems that I am able to pull a pretty even vacuum on the test samples. But I feel that the board will need a breather fabric to acchieve an even vacuum distribution since it has a much larger surface area.

The air pressure will most certainly be enough to from the rocker Zob; surface area is around 0.5 m^2. Assuming a 90% vacuum gives an air pressure of 90000 N/m^2. This gives a force of 45000 Newton on the board which is equivalent to a mass of 4500 kg. But, I am using a bag! So I need to get creative with some clamps.

I don't really understand the thing about the waterline and the need for a strong topsheet downunder. Could you please explain? I have a nylon topsheet which I will probably use.

Do you guys have any tips/recommendations for the edges? I feel like the fiberglass+epoxy layer will be exposed to the water since it is laying on top of the sidewall... How to prevent delaminations. My current wakeboard somehow sealed the edge all the way from the base to the topsheet.

skriever wrote:
Do you guys have any tips/recommendations for the edges? I feel like the fiberglass+epoxy layer will be exposed to the water since it is laying on top of the sidewall... How to prevent delaminations. My current wakeboard somehow sealed the edge all the way from the base to the topsheet.

Yes the fg + epoxy layer is exposed to water and that is fine. Its entire purpose is to be exposed to the water so that the core isn't.
The epoxy laminate on top and bottom seal against the rail and protects the core.

Provided you prepared the rail for bonding, you are unlikely to have any delaminations. And even if you didn't, you're still unlikely to have delaminations. Typical board construction is a pretty robust process and properly mixed and cured epoxy is plenty strong.

Delaminations are more likely with a UHMWPE base, which has known bonding issues and requires more careful preparation. But even then, you would have to really try hard to make it delaminate.

Strong topsheet is not nylon. Nylon does not stick to epoxy and it might be dissolved...The topsheet is at the board bottom, what I call a waterline. Can be on top as well, but it's a waste of time for DIY.

You can't apply a topsheet with a vac expecting no air trapped below. Simple impossible. I was thinking to perforate the board with tiny holes to be able to do that, but just too much work with no gain since a thick epoxy layer can do just fine. But, a thick epoxy layer is a Holly Grail of DIY building, hence a number of thinner layers.

Interesting stuff . But you guys aren't worried about the water absorbtion of epoxy over time? I have no clue how severe the absorption will be in practice. But considering your reply's I guess it won't be that critical. I dont like drilling holes in core for aesthetic reasons and possible loss of mechanical strength. I can think of 2 glassing sequences. Do you guys see any other potential dangers?

Number 1:
1. Set rocker of table to 11 cm.
2. Glass top face (FG+epoxy only) to core in vacbag. Must be clamped to the rocker table. Let the board spring back (hoping for 5-6 cm rocker). Top side is in tension so is the best side for letting the board springback
3. Adjust the rocker table to the current rocker of the cured core+topface. Alternatively, rocker can be adjusted a little bit to the desired rocker if the springback is more or less then the expected value
4. Create the bottomface by curing the ptex base+FG in the vacbag on the rocker table with the correct amount of rocker (WITHOUT the core). Only way, because air will get trapped between ptex-base and core if glassed in single step.
Besides, letting the core springback with the ptex base attached doesn't feels like a good idea... Compressive stresses might cause the base to delaminate from the core.
5. Add the ptex-base+FG to the core+FG with a (relative) thin layer of epoxy and letting it cure once again. Hoping that air bubbles wont get trapped
Dangers: Core might warp after step 2.

Number 2:
1. Set rocker of table to 9-10 cm.
2. Glass both top face and bottom face to core in 1 go (FG only) in vacbag. Must be clamped to the rocker table. Let the board spring back (hoping for 5-6 cm rocker). Top face is under tension and bottom face under compression.
Both top and bottom face resist the springback of the core, so less 'pre'-rocker is necessary
3. Adjust the rocker table to the current rocker of the cured bottom-face+core+top-face.
4. Add the ptex-base to the bottom with a (relative) thin layer of epoxy. Hoping that air bubbles wont get trapped
Dangers for number 2:
-A lot of resin needs to mixed for the second step.
-Rocker after springback is final.
-Bottom face more difficult to apply in step 2 because I would like to roll out any air bubbles before applying vacuum.

Setting a table with 1-2cm difference with a wood core is questionable in my opinion. The result rocker of 5-6cm is huge expectation tho even for 140cm board.

#1.3 After the springback you can't do anything unless you're glassing the top again (with more rocker). Hence, for glassing the bottom no need for a rocker table at all. Use a vac bag only. This is my experience, others can advice.
#1.4 Your sheet will be wobbly as hell. You're creating a pre-cured topsheet basically with almost no thickness.

#2.2
If you clamp a vac bag on a rocker table that might imprint on board (your 6th pic with a clamps). Very difficult to fix after. For sure bottom is compressed but that is your enemy. It might wrap a FG on numerous places. If it does, that is not fixable.
#2.4 not a thin layer tho.

Just build it, and see how it works for you. There is no substitute for experience, and repetition is a mother of ...

I still think you should consider kerfing the core. Sounds like a lot less hassle than any of the other proposals. Since your doing a wood core anyway, the extra weight of the resin won't be significant.

It has been a while, busy doing other stuff. My personal deadline for the board is 31 December

I made some more test samples a few weeks ago. I experimented with bleeders breathers and peelply. I only got good results (as far as I can tell) when using the peel ply only. The breather simply absorbed all of the resin during vac bagging I found that the breather (150 g/m^2) absorbed 345 g/m^2 and that the peelply (95 g/m^2) absorbed 45 g/m^2 resin. I could use a bleeder with less/smaller holes to reduce the resin absorption by the breather. But, I need to stop experimenting and start building. So I go for peelply only.

Look at this cool tool ...

I used some insulation foam plates to build an oven to (hopefully) improve the quality of the board. I used an old climate control unit to regulate the temperature to the desired value. A heat gun serves as the heat source which is connected to the climate controle unit via a relay. Best thing; I didn't need to spend any money on the oven (I am dutch )

The board is now sitting in the rocker table waiting to be glassed. The pre-rocker is now set to 11 cm. I was hoping that the stresses in the core relax a bit over time. It will be glassed in about 7 days or so.

Ps. Anybody has a though on a good temperature for the oven during curing? I was thinking 50 degrees celcius...
Ps2: I thick kerfing would mess with the structual integrity of the board, I will go for some exaggerated pre-rocker.

My oven is very similar. 5cm thick ceiling insulation panels. I use two 100W light bulbs for heating, and a dimmer switch for control.
Check your resin spec sheet for the curing schedule. Mine is 50C for 16h.
Maybe do a dry run with your oven first. A heat gun puts out a LOT of heat, beware of fire risk.

Been there mate. Burned the board. No oven for me any more. The silicone blanket(s) all the way. The problem with a oven for me was a rocker table, how to put one in the oven?
The silicone blanket you just slap on your work, it will conform to the curved area, and a PID will control it. The blanket cost is about $30-40.

I do not bother leaving a running blanket for more than 4-5hrs on 45C. In reality, if the epoxy is not made for a hot curing, no need for it, no benefits as I understand. Except faster curing in a cold climate:)

$30-40 is not to expensive and is probably a more elegant solution. Something to consider for a future build.

Ps. The supplier of my resin warned me that 50 degrees is way to much for my particular resin since the epoxy would degas at this temperature (the temperatue and heat generation of the epoxy act like a snowballeffect). They advised me to increase the temperature only a few degrees beacause this could make a huge difference in terms of better impregnation and bonding. I think I will start with 25 degrees then

Last edited by skriever on Wed Dec 21, 2016 1:31 pm, edited 4 times in total.